Alumina interaction with lead

Several products other than 2,2 -biaryls have been isolated following reaction of pyridines with metal catalysts. From the reaction of a-picoline with nickel-alumina, Willink and Wibaut isolated three dimethylbipyridines in addition to the 6,6 -dimethyl-2,2 -bipyridine but their structures have not been elucidated. From the reaction of quinaldine with palladium-on-carbon, Rapoport and his co-workers " obtained a by-product which they regarded as l,2-di(2-quinolyl)-ethane. From the reactions of pyridines and quinolines with degassed Raney nickel several different types of by-product have been identified. The structures and modes of formation of these compounds are of interest as they lead to a better insight into the processes occurring when pyridines interact with metal catalysts. 

This paper describes the catalytic activity of nickel phosphide supported on silica, alumina, and carbon-coated alumina in the hydrodesulfurization of 4,6-dimethyldibenzothiophene. The catalysts are made by the reduction of phosphate precursors. On the silica support the phosphate is reduced easily to form nickel phosphide with hi catalytic activity, but on the alumina support interactions between the phosphate and the alumina hinder the reduction. The addition of a carbon overlayer on alumina decreases the interactions and leads to the formation of an active phosphide phase. 

Diphenylmercury interacts with nickel supported on alumina, under H2 and in heptane solution, at 373 K, to give mostly biphenyl and metallic mercury. During the reaction, Hg induces leaching of nickel, which leads to a progressive deactivation of the catalyst (Scheme 2.42) [126]. 

These results indicate that alumina acts on CrgOg phase to prevent its clustering and segregation with high coordinate Cr + ions. This dispersive effect of the support provides a suitable environment for the formation on the surface of low coordinate chromium ions (ref. 2). However this effect of alumina tends to depress when the content of chromium exceeds 30 % at 410°C. This result seems to Indicate a saturation of the surface sites of the support which interact with the chromium (surface of alumina covered with a layer of chromium oxide). Then an excess of Cr O deposited leads to its clustering and crystallization. Consequently the coordination of chromium ions changes from tetrahedral (low coordination) to octahedral (high coordination). 

Hohl, H. and Stumm, W. (1976) Interaction of lead(2+) with hydrous y-alumina.J. Coll. Interface Sci., 55, 281-288. 

The actual magnitude of the interaction of a given substituent with the adsorbent depends on the adsorbent, other substituents present, and the type and rigidity of the backbone of the diastereomeric analytes. Although no serious attempts at quantification have been made, repulsive interactions toward silica and alumina can be ranked roughly as H < methyl < phenyl = ethyl < tert-butyl < triliuoromethyl < a-naphthyl < 9-anthryl = pentafluoroethyl < heptaliuoroethyl. Size and hydrophobicity are both relevant incorporation of polar functionality (hydroxyl, carbalkoxy, cyano) leads to attractive rather than repulsive interactions with silica. 

Nickel and vanadium are contained within the crude oil as their respective porphyrins and napthenates (2). As these large molecules are cracked, the metals are deposited on the catalyst. Nickel which possesses a high intrinsic dehydrogenation and hydrogenolysis activity drastically increases the production of coke and dry gas (particularly H2) at the expense of gasoline. Vanadium on the other hand interacts with the zeolitic component of a cracking catalyst and leads to destruction of its crystallinity. This results in reduced activity as well as an increase in non-selective amorphous silica-alumina type cracking. Supported vanadium also has an intrinsic... 

Pyridine adsorption at room temperature on activated cloverite evidences the presence of Lewis and Bronsted acid sites. Pyridinium species hardly persists after evacuation at 423 K, showing that the Bronsted acidity is not very strong. Spectra analysis confirms that pyridinium species occur from the interaction with P-OH groups since the 3673 cm- and 944 cm- bands are regenerated by heating at the expense of the pyridinium species. The 3700 cm- v(OH) band hardly reappears by thermal evacuation suggesting that an irreversible reaction occurs during this treatment. Note that pyridine adsorption on phosphated alumina leads to protonation (8) due to interaction with free POH hydroxyls. 

An extensive literature exists on the characterization and structure—activity correlation of industrial copper-alumina oxychlorination catalysts [95-120]. At least two different major copper species have been identified. At low concentrations of copper (below ca 5 %), a well-dispersed copper species in intimate interaction with the alumina surface is formed. This species has a very low oxychlorination activity. At higher concentrations, a second species, probably formed by the de-position/precipitation of the copper chloro complexes, is observed. The latter gives rise to the active sites during the oxychlorination reaction. On the basis of an FTIR study of the oxychlorination reaction Finocchio et al. [42] postulated the formation of surface copper chloride-ethylene r-complex intermediates (which lead eventually to EDC) and weakly adsorbed HCl during oxychlorination. Formate species associated with copper and probable precursors for formation of the oxides of carbon by combustion were also identified. 

---